Hybrid Attitude Control of a Two-CubeSat Virtual Telescope in a Highly Elliptical Orbit
Session
Session 10: Leo Missons
Abstract
The Virtual telescope for X-ray observation (VTXO) is a mission exploiting two 6U-CubeSats operating in precision formation. The goal of the VTXO research is to develop a space-based, X-ray imaging telescope with sub-arcsecond angular resolution. In the scheme, one CubeSat carries a diffractive lens and the other one carries an imaging device to support focal lengths from 100m to 1 km. In this mission, the Guidance, navigation and control (GN&C) algorithms are required to keep the two spacecraft in alignment while collecting data. In the VTXO mission, we have three major phases including the open-loop formation phase, the development phase, and the scientific phase. In the open-loop formation phase, no attitude control is performed and the two satellites pass the perigee to achieve the development phase. In the next phase, the development phase, the coarse pre-attitude control is performed to provide enough attitude determination for the scientific phase. In the scientific phase, the precision attitude control takes place. In this phase, the two satellites point at the Crab Nebula or the Sun. This phase takes place in the apogee since there is more time in the apogee, comparing to the other parts of the orbit, and the two satellites move more slowly, which results in a more precise attitude control. In this paper, attitude control is exploited based on the quaternion model of the two satellites. In this model, the gravitational and the atmospheric drag perturbations are considered. In the attitude control design of the system, the noises of different sensors, including the astrometric sensor, the IMU sensor, and the star tracker, are considered and the navigation part of the control system uses a filter to approximate the relative velocity and position of the two satellites based on the noisy data from the sensors. In the attitude control system, each phase has to be stable and the duration of each phase has to be designed based on the stability of each phase, the stability of the whole system and the desired sub-arcsecond angular resolution in the scientific phase with all the noises and the perturbations in the system. Considering all the previously mentioned criteria involved in the attitude control deign and the three different phases in the attitude control, hybrid control techniques are investigated in this paper for the attitude control design, due to the fact that hybrid control has the capacity to satisfy the given criteria and can include different stages in control.
Presentation
Hybrid Attitude Control of a Two-CubeSat Virtual Telescope in a Highly Elliptical Orbit
The Virtual telescope for X-ray observation (VTXO) is a mission exploiting two 6U-CubeSats operating in precision formation. The goal of the VTXO research is to develop a space-based, X-ray imaging telescope with sub-arcsecond angular resolution. In the scheme, one CubeSat carries a diffractive lens and the other one carries an imaging device to support focal lengths from 100m to 1 km. In this mission, the Guidance, navigation and control (GN&C) algorithms are required to keep the two spacecraft in alignment while collecting data. In the VTXO mission, we have three major phases including the open-loop formation phase, the development phase, and the scientific phase. In the open-loop formation phase, no attitude control is performed and the two satellites pass the perigee to achieve the development phase. In the next phase, the development phase, the coarse pre-attitude control is performed to provide enough attitude determination for the scientific phase. In the scientific phase, the precision attitude control takes place. In this phase, the two satellites point at the Crab Nebula or the Sun. This phase takes place in the apogee since there is more time in the apogee, comparing to the other parts of the orbit, and the two satellites move more slowly, which results in a more precise attitude control. In this paper, attitude control is exploited based on the quaternion model of the two satellites. In this model, the gravitational and the atmospheric drag perturbations are considered. In the attitude control design of the system, the noises of different sensors, including the astrometric sensor, the IMU sensor, and the star tracker, are considered and the navigation part of the control system uses a filter to approximate the relative velocity and position of the two satellites based on the noisy data from the sensors. In the attitude control system, each phase has to be stable and the duration of each phase has to be designed based on the stability of each phase, the stability of the whole system and the desired sub-arcsecond angular resolution in the scientific phase with all the noises and the perturbations in the system. Considering all the previously mentioned criteria involved in the attitude control deign and the three different phases in the attitude control, hybrid control techniques are investigated in this paper for the attitude control design, due to the fact that hybrid control has the capacity to satisfy the given criteria and can include different stages in control.
